Multi-chip light emitting device lamps for providing high-CRI warm white light and light fixtures including the same

ABSTRACT

A multi-chip lighting emitting device (LED) lamp for providing white light includes a submount including first and second die mounting regions thereon. A first LED chip is mounted on the first die mounting region, and a second LED chip is mounted on the second die mounting region. The LED lamp is configured to emit light having a spectral distribution including at least four different color peaks to provide the white light. For example, a first conversion material may at least partially cover the first LED chip, and may be configured to absorb at least some of the light of the first color and re-emit light of a third color. In addition, a second conversion material may at least partially cover the first and/or second LED chips, and may be configured to absorb at least some of the light of the first and/or second colors and re-emit light of a fourth color. Related light fixtures and methods are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 11/743,324filed May 2, 2007 and published as U.S. Patent Application PublicationNo. 2007/0223219, which is a continuation-in-part of U.S. patentapplication Ser. No. 11/032,363 filed Jan. 10, 2005, subsequently issuedas U.S. Pat. No. 7,564,180 on Jul. 21, 2009. The disclosures of all ofthe foregoing applications are hereby incorporated herein by referencein their respective entireties, for all purposes, and the priority ofall such applications is hereby claimed under the provisions of 35 USC120.

TECHNICAL FIELD

This invention relates to semiconductor light emitting devices, and moreparticularly, to multi-chip semiconductor light emitting devicesincluding wavelength conversion materials and related devices.

BACKGROUND

Light emitting diodes and laser diodes are well known solid statelighting elements capable of generating light upon application of asufficient voltage. Light emitting diodes and laser diodes may begenerally referred to as light emitting devices (“LEDs”). Light emittingdevices generally include a p-n junction formed in an epitaxial layergrown on a substrate such as sapphire, silicon, silicon carbide, galliumarsenide and the like. The wavelength distribution of the lightgenerated by the LED generally depends on the material from which thep-n junction is fabricated and the structure of the thin epitaxiallayers that make up the active region of the device

Typically, an LED chip includes a substrate, an n-type epitaxial regionformed on the substrate and a p-type epitaxial region formed on then-type epitaxial region (or vice-versa). In order to facilitate theapplication of a voltage to the device, an anode ohmic contact may beformed on a p-type region of the device (typically, an exposed p-typeepitaxial layer) and a cathode ohmic contact may be formed on an n-typeregion of the device (such as the substrate or an exposed n-typeepitaxial layer).

LEDs may be used in lighting/illumination applications, for example, asa replacement for conventional incandescent and/or fluorescent lighting.As such, it is often desirable to provide a lighting source thatgenerates white light having a relatively high color rendering index(CRI), so that objects illuminated by the lighting may appear morenatural. The color rendering index of a light source is an objectivemeasure of the ability of the light generated by the source toaccurately illuminate a broad range of colors. The color rendering indexranges from essentially zero for monochromatic sources to nearly 100 forincandescent sources. The color quality scale (CQS) is another objectivemeasure for assessing the quality of light, and similarly ranges fromessentially zero to nearly 100.

In addition, the chromaticity of a particular light source may bereferred to as the “color point” of the source. For a white lightsource, the chromaticity may be referred to as the “white point” of thesource. The white point of a white light source may fall along a locusof chromaticity points corresponding to the color of light emitted by ablack-body radiator heated to a given temperature. Accordingly, a whitepoint may be identified by a correlated color temperature (CCT) of thelight source, which is the temperature at which the heated black-bodyradiator matches the color or hue of the white light source. White lighttypically has a CCT of between about 4000 and 8000 K. White light with aCCT of 4000 has a yellowish color. White light with a CCT of 8000 K ismore bluish in color, and may be referred to as “cool white”. “Warmwhite” may be used to describe white light with a CCT of between about2600 K and 6000 K, which is more reddish in color.

In order to produce white light, multiple LEDs emitting light ofdifferent colors of light may be used. The light emitted by the LEDs maybe combined to produce a desired intensity and/or color of white light.For example, when red-, green- and blue-emitting LEDs are energizedsimultaneously, the resulting combined light may appear white, or nearlywhite, depending on the relative intensities of the component red, greenand blue sources. However, in LED lamps including red, green, and blueLEDs, the spectral power distributions of the component LEDs may berelatively narrow (e.g., about 10-30 nm full width at half maximum(FWHM)). While it may be possible to achieve fairly high luminousefficacy and/or color rendering with such lamps, wavelength ranges mayexist in which it may be difficult to obtain high efficiency (e.g.,approximately 550 nm).

In addition, the light from a single-color LED may be converted to whitelight by surrounding the LED with a wavelength conversion material, suchas phosphor particles. The term “phosphor” may be used herein to referto any materials that absorb light at one wavelength and re-emit lightat a different wavelength, regardless of the delay between absorptionand re-emission and regardless of the wavelengths involved. Accordingly,the term “phosphor” may be used herein to refer to materials that aresometimes called fluorescent and/or phosphorescent. In general,phosphors absorb light having shorter wavelengths and re-emit lighthaving longer wavelengths. As such, some or all of the light emitted bythe LED at a first wavelength may be absorbed by the phosphor particles,which may responsively emit light at a second wavelength. For example, asingle blue emitting LED may be surrounded with a yellow phosphor, suchas cerium-doped yttrium aluminum garnet (YAG). The resulting light,which is a combination of blue light and yellow light, may appear whiteto an observer.

However, light generated from a phosphor-based solid state light sourcemay have a relatively low CRI. In addition, while light generated bysuch an arrangement may appear white, objects illuminated by such lightmay not appear to have natural coloring due to the limited spectrum ofthe light. For example, as the light from a blue LED covered by a yellowphosphor may have little energy in the red portion of the visiblespectrum, red colors in an object may not be well-illuminated. As aresult, the object may appear to have an unnatural coloring when viewedunder such a light source. Accordingly, it is known to include somered-emitting phosphor particles to improve the color renderingproperties of the light, i.e., to make the light appear more “warm”.However, over time, the red-emitting phosphor particles may be subjectto greater degradation than the yellow-emitting phosphor particles,which may decrease the useful lifetime of the light source.

Accordingly, there is a continued need for improved LED lighting sourcesfor general illumination.

SUMMARY

A solid state lamp according to one aspect of the invention includes afirst solid state emitter having peak emissions within a blue wavelengthrange; a second solid state emitter having peak emissions within a cyanwavelength range; a first wavelength conversion material at leastpartially covering the first solid state emitter and arranged to emitlight within a yellow wavelength range; and a second wavelengthconversion material at least partially covering the second solid stateemitter and arranged to emit light within a red wavelength range.

A solid state lamp according to another aspect of the invention includesa plurality of solid state emitters including a first solid stateemitter having peak emissions within a blue wavelength range, a secondsolid state emitter having peak emissions within a cyan wavelengthrange, and a third solid state emitter having peak emissions within agreen wavelength range; and a first wavelength conversion material atleast partially covering each emitter of the plurality of solid stateemitters and arranged to emit light within a yellow wavelength range.

A multi-chip light emitting device (LED) lamp for providing white lightaccording to some embodiments of the invention includes a submountincluding first and second die mounting regions. A first LED chip ismounted on the first die mounting region, and a second LED chip ismounted on the second die mounting region. The LED lamp is configured toemit light having a spectral distribution including at least fourdifferent color peaks to provide the white light. In some embodiments,the first and second LED chips are configured to emit light of a samecolor. In other embodiments, the first LED chip is configured to emitlight of a first color, and the second LED chip is configured to emitlight of a second color.

In some embodiments, the lamp may include a first conversion material atleast partially covering the first LED chip and configured to absorb atleast some of the light of the first color and re-emit light of a thirdcolor. In addition, the lamp may include a second conversion material atleast partially covering the first and/or second LED chips andconfigured to absorb at least some of the light of the first and/orsecond colors and re-emit light of a fourth color. In some embodiments,the coverage of the first and second conversion materials may notoverlap.

In other embodiments, the first and second conversion materials may beconfigured to re-emit light having a greater wavelength than that of thelight emitted by the first and/or second LED chips. For example, thefirst LED chip may be configured to emit light within a blue wavelengthrange, the second LED chip may be configured to emit light within a cyanwavelength range, the first conversion material may be a yellow-emittingphosphor, and the second conversion material, may be a red-emittingphosphor.

In some embodiments, the first conversion material may be a firstsemiconductor layer on the first LED chip, and the second conversionmaterial may be a second semiconductor layer on the second LED chip. Thefirst and second semiconductor layers may have respective bandgaps thatare narrower than those of quantum wells of the first and second LEDchips. The first and/or second semiconductor layers may further includea quantum well structure.

In other embodiments, the submount may further include a third diemounting region thereon, and the lamp may include a third LED chipmounted on the third die mounting region. The third LED chip may beconfigured to emit light of a third color. A conversion material may atleast partially cover the first LED chip, and may be configured toabsorb at least some of the light of the first color and re-emit lightof a fourth color.

In some embodiments, the third LED chip may be configured to emit lighthaving a wavelength greater than that of the second LED chip. Inaddition, the second LED chip may be configured to emit light having awavelength greater than that of the first LED chip. The conversionmaterial may be configured to re-emit light having a wavelength betweenthat of the second LED chip and that of the third LED chip.

In other embodiments, the first LED chip may be configured to emit lightwithin a blue wavelength range, the second LED chip may be configured toemit light within a cyan wavelength range, and the third LED chip may beconfigured to emit light within a red wavelength range.

In some embodiments, the conversion material may be a yellow-emittingphosphor. For example, the conversion material may be yttrium aluminumgarnet.

In other embodiments, the first LED chip may be configured to emit lightat a peak wavelength of about 440-470 nm, the second LED chip may beconfigured to emit light at a peak wavelength of about 495-515 nm, andthe third LED chip may be configured to emit light at a peak wavelengthof about 610-630 nm.

In some embodiments, a combination of the light emitted from the first,second, and third LED chips and the conversion material may have anaverage wavelength of about 555 nm. Also, a combination of the lightemitted from the first, second, and third LED chips and the conversionmaterial may have a color temperature of about 2600 K to about 6000 K.Furthermore, a combination of the light emitted from the first, second,and third LED chips and the conversion material may have acolor-rendering index (CRI) of about 90-99.

According to other embodiments of the present invention, a lightemitting device (LED) light fixture for providing white light includes amounting plate and a plurality of multi-chip LED lamps attached to themounting plate. Each of the plurality of multi-chip LED lamps includes asubmount including first and second die mounting regions thereonattached to the mounting plate. A first LED chip configured to emitlight of a first color is mounted on the first die mounting region, anda second LED chip configured to emit light of a second color is mountedon the second die mounting region of the submount. At least one of theplurality of multi-chip LED lamps is configured to emit light having aspectral distribution including at least four different color peaks toprovide the white light.

In some embodiments, the at least one of the plurality of multi-chip LEDlamps may further include first and second conversion materials. Thefirst conversion material may at least partially cover the first LEDchip, and may be configured to absorb at least some of the light of thefirst color and re-emit light of a third color. The second conversionmaterial may at least partially cover the first and/or second LED chips,and may be configured to absorb at least some of the light of the firstand/or second colors and re-emit light of a fourth color.

In other embodiments, the at least one of the plurality of multi-chipLED lamps may further include a third LED chip configured to emit lightof a third color mounted on a third die mounting region of the submount.In addition, a conversion material may at least partially cover thefirst LED chip, and may be configured to absorb at least some of thelight of the first color and re-emit light of a fourth color.

In some embodiments, the first, second, and third LED chips of ones ofthe plurality of multi-chip LED lamps may be individually addressable.In addition, the LED light fixture may further include a control circuitelectrically coupled to the plurality of multi-chip LED lamps. Thecontrol circuit may be configured to respectively apply first, second,and third drive currents to the first, second, and third LED chips inones of the plurality of multi-chip LED lamps at a predetermined currentratio. For example, the control circuit may be configured toindependently apply first, second, third, and/or fourth drive currentsto first, second, third, and/or fourth LED chips at a ratio depending onthe brightness and/or wavelength(s) of the LED chip(s) and/or on thebrightness and/or wavelengths of the converted light from the conversionmaterial(s) to achieve desired color coordinates and/or color point. Assuch, a combination of the light emitted from the first, second, andthird LED chips and the phosphor coating may have a color temperature ofabout 2600 K to about 6000 K, an average wavelength of about 555 nm,and/or a color-rendering index (CRI) of about 95.

In other embodiments, the light fixture may further include at least onesingle-chip LED lamp attached to the mounting plate adjacent theplurality of multi-chip LED lamps.

According to further embodiments of the present invention, a multi-chiplight emitting device (LED) lamp for providing white light includes asubmount including first and second die mounting regions thereon. A blueLED chip is mounted on the first die mounting region and is configuredto emit light within a blue wavelength range responsive to a first biascurrent. A cyan LED chip is mounted on the second die mounting regionand is configured to emit light within a red wavelength range responsiveto a second bias current. A phosphor material at least partially coversthe blue LED chip and is configured to convert at least some of thelight within the blue wavelength range to light within a yellowwavelength range.

In some embodiments, a second phosphor material at least partiallycovers the cyan LED chip and may be configured to convert at least someof the light within the cyan wavelength range to light within a redwavelength range.

In other embodiments, a red LED chip may be mounted on a third diemounting region and may be configured to emit light within a cyanwavelength range responsive to a third bias current.

According to still further embodiments of the present invention, amethod of operating a multi-element light emitting device (LED) lamphaving blue, cyan, and red LED chips includes independently applyingfirst, second, and third drive currents to the blue, cyan, and red LEDchips. As such, a combination of the light emitted from the blue, cyan,and red LED chips may provide white light having a color temperature ofabout 2600 K to about 6000 K, an average wavelength of about 555 nm,and/or a color-rendering index (CRI) of about 90-99.

According to still further embodiments of the present invention, amulti-chip light emitting device (LED) lamp for providing white lightincludes a submount including a die mounting region thereon, an LED chipmounted on the die mounting region and configured to emit light of afirst color, and a semiconductor layer on the LED chip. Thesemiconductor layer is configured to absorb at least some of the lightof the first color and re-emit light of another color. The semiconductorlayer may be a direct bandgap semiconductor material having a narrowerbandgap than that of quantum wells of the LED chip. In some embodiments,the semiconductor layer may include a quantum well structure.

Other aspects, features and embodiments of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top view illustrating a light emitting device light fixtureaccording to some embodiments of the invention.

FIG. 1B is a top view illustrating a light emitting device light fixtureaccording to further embodiments of the invention.

FIGS. 2A-2D are top views illustrating light emitting device lampsaccording to some embodiments of the invention.

FIGS. 3A-3F are top views illustrating light emitting device lampsaccording to further embodiments of the invention.

FIGS. 4A-4B are graphs illustrating the spectral distribution of lightemitted by individual light emitting devices in light emitting devicelamps according to some embodiments of the invention.

FIG. 5 is a chromaticity diagram illustrating the chromaticity of lightemitted by light emitting device lamps according to some embodiments ofthe invention.

FIG. 6 is a flowchart illustrating methods for operating light emittingdevice lamps according to some embodiments of the invention.

FIGS. 7A-7D are side views illustrating light emitting device lampsaccording to still further embodiments of the invention.

FIG. 8 is an energy diagram illustrating characteristics of directbandgap semiconductor phosphor layers for use in light emitting devicelamps according to still further embodiments of the invention.

DETAILED DESCRIPTION

The present invention now will be described more fully with reference tothe accompanying drawings, in which embodiments of the invention areshown. This invention may, however, be embodied in many different formsand should not be construed as limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art. In the drawings, the size andrelative sizes of layers and regions may be exaggerated for clarity.Like numbers refer to like elements throughout.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. It will be understood that if part of an element, such as asurface, is referred to as “inner,” it is farther from the outside ofthe device than other parts of the element. Furthermore, relative termssuch as “beneath” or “overlies” may be used herein to describe arelationship of one layer or region to another layer or region relativeto a substrate or base layer as illustrated in the figures. It will beunderstood that these terms are intended to encompass differentorientations of the device in addition to the orientation depicted inthe figures. Finally, the term “directly” means that there are nointervening elements. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the present invention.

Embodiments of the invention are described herein with reference tocross-sectional, perspective, and/or plan view illustrations that areschematic illustrations of idealized embodiments of the invention. Assuch, variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, embodiments of the invention should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing. For example, a region illustrated or described as arectangle will, typically, have rounded or curved features due to normalmanufacturing tolerances. Thus, the regions illustrated in the figuresare schematic in nature and their shapes are not intended to illustratethe precise shape of a region of a device and are not intended to limitthe scope of the invention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andthis specification and will not be interpreted in an idealized or overlyformal sense unless expressly so defined herein.

As used herein, the term “semiconductor light emitting device” and/or“LED” may include a light emitting diode, laser diode and/or othersemiconductor device which includes one or more semiconductor layers,which may include silicon, silicon carbide, gallium nitride and/or othersemiconductor materials. A light emitting device may or may not includea substrate such as a sapphire, silicon, silicon carbide and/or anothermicroelectronic substrates. A light emitting device may include one ormore contact layers which may include metal and/or other conductivelayers. In some embodiments, ultraviolet, blue, cyan, and/or green lightemitting diodes may be provided. Red and/or amber LEDs may also beprovided. The design and fabrication of semiconductor light emittingdevices are well known to those having skill in the art and need not bedescribed in detail herein.

For example, the semiconductor light emitting device may be galliumnitride-based LEDs or lasers fabricated on a silicon carbide substratesuch as those devices manufactured and sold by Cree, Inc. of Durham,N.C. Some embodiments of the present invention may use LEDs and/orlasers as described in U.S. Pat. Nos. 6,201,262; 6,187,606; 6,120,600;5,912,477; 5,739,554; 5,631,190; 5,604,135; 5,523,589; 5,416,342;5,393,993; 5,338,944; 5,210,051; 5,027,168; 5,027,168; 4,966,862 and/or4,918,497, the disclosures of which are incorporated herein by referenceas if set forth fully herein. Other suitable LEDs and/or lasers aredescribed in U.S. Pat. No. 6,958,497 entitled Group III Nitride BasedLight Emitting Diode Structures With a Quantum Well and Superlattice,Group III Nitride Based Quantum Well Structures and Group III NitrideBased Superlattice Structures, as well as U.S. Pat. No. 6,791,119entitled Light Emitting Diodes Including Modifications for LightExtraction and Manufacturing Methods Therefor. Furthermore, phosphorcoated LEDs, such as those described in U.S. Pat. No. 6,853,010,entitled Phosphor-Coated Light Emitting Diodes Including TaperedSidewalls and Fabrication Methods Therefor, the disclosure of which isincorporated by reference herein as if set forth fully, may also besuitable for use in embodiments of the present invention. The LEDsand/or lasers may also be configured to operate such that light emissionoccurs through the substrate.

Some embodiments of the present invention provide multi-chip LED lampsand related light fixtures for high brightness applications, such asrecessed or “can” lighting. LED light fixtures according to someembodiments of the present invention may offer longer life and/orgreater energy efficiency, and may provide white light output that iscomparable to that of conventional light sources, such as incandescentand/or fluorescent light sources. In addition, LED light fixturesaccording to some embodiments of the present invention may match and/orexceed the brightness output, performance, and/or CRI of conventionallight sources, while maintaining a similar fixture size.

FIGS. 1A and 1B illustrate LED light fixtures according to someembodiments of the present invention. Referring now to FIG. 1A, a lightfixture 100 a includes a mounting plate 105 including multiplemulti-chip LED lamps 110 attached to the mounting plate 105. Althoughillustrated as having a circular shape, the mounting plate 105 may beprovided in other shapes as well. As used herein, a “multi-chip LEDlamp” includes at least two LED chips, each of which may be configuredto emit the same or different colors of light, mounted on a commonsubstrate or submount. As shown in FIG. 1A, each multi-chip LED lamp 110includes four LED chips 103 mounted on a common submount 101. In someembodiments, one or more of the multi-chip LED lamps 110 may beconfigured to provide white light based on the combination of the colorsof light emitted by each of its component LED chips 103. For example,one or more of the multi-chip LED lamps 110 may be configured to emitlight having a spectral distribution including at least four differentcolor peaks (i.e., having local peak wavelengths in wavelength rangescorresponding to at least four different colors of light) to provide thewhite light. Examples of LED color combinations in multi-chip lampsaccording to some embodiments of the present invention will be providedbelow with reference to FIGS. 2A-2D and FIGS. 3A-3E. The multi-chiplamps 110 may be grouped on the mounting plate 105 in clusters and/orother arrangements such that the light fixture 100 a outputs a desiredpattern of light.

Still referring to FIG. 1A, the light fixture 100 a further includes acontrol circuit 150 a electrically coupled to each of the multi-chip LEDlamps 110. The control circuit is configured to operate the lamps 110 byindependently applying drive currents to the individual LED chips 103 ineach lamp 110. In other words, each of the LED chips 103 in each lamp110 may be configured to be individually addressed by the controlcircuit 150 a. For example, the control circuit 150 a may include acurrent supply circuit configured to independently apply an on-statedrive current to each of the individual LED chips 103 responsive to acontrol signal, and a control system configured to selectively providethe control signals to the current supply circuit. As LEDs arecurrent-controlled devices, the intensity of the light emitted from anLED is related to the amount of current driven through the LED. Forexample, one common method for controlling the current driven through anLED to achieve desired intensity and/or color mixing is a Pulse WidthModulation (PWM) scheme, which alternately pulses the LEDs to a fullcurrent “ON” state followed by a zero current “OFF” state. Accordingly,the control circuit 150 a may be configured to control the currentdriven through the LED chips 103 using one or more control schemes asare well known in the art.

While not illustrated in FIG. 1A, the light fixture 100 a may furtherinclude one or more heat spreading components and/or sinks for spreadingand/or removing heat emitted by the LED chips 103. For example, a heatspreading component may include a sheet of thermally conductive materialhaving an area and configured to conduct heat generated by the LED chips103 of the light fixture 100 a and spread the conducted heat over thearea of the mounting plate 105 to reduce thermal nonuniformities in thelight fixture 100 a. The heat spreading component may be a solidmaterial, a honeycomb or other mesh material, an anisotropic thermallyconductive material, such as graphite, and/or other materials.

FIG. 1B illustrates an LED light fixture 100 b according to furtherembodiments of the present invention. As shown in FIG. 1B, the lightfixture 100 b includes a mounting plate 105 and a plurality ofmulti-chip LED lamps 110 attached to the mounting plate 105 in anarrangement and/or pattern selected to provide a desired light output,similar to that of the LED light fixture 100 a of FIG. 1A. The lightfixture 100 b further includes one or more single-chip LED lampsattached to the mounting plate 105 in combination with the multi-chiplamps 110. As used herein, a “single-chip LED lamp” refers to an LEDlamp including only one LED chip. For example, one single-chip LED lampmay be included in each grouping of multi-chip LED lamps to provide upto a 2 to 4:1 ratio of multi-chip LED lamps to single-chip LED lamps.However, depending on the desired color point, the ratio may be higheror lower.

More particularly, as illustrated in FIG. 1B, the light fixture 100 bincludes two single-chip LED lamps 106 r and 106 c. The lamp 106 r isconfigured to emit light in a red wavelength range (e.g., 610-630 nm),while the lamp 106 c is configured to emit light in a cyan wavelengthrange (e.g., 485-515 nm). However, single-chip LED lamps configured toemit light of other colors may also be provided in light fixturesaccording to some embodiments of the present invention. The single-chipLED lamps 106 r and/or 106 c may be used to adjust the CRI and or CCT ofthe light output by the light fixture 100 b. For example, the lamp 106 rmay be used to provide additional light in the red wavelength range suchthat the overall light provided by the light fixture 100 b may appear tobe a “warmer” color of white light. More particularly, the white lightoutput by the LED light fixture 100 b may have a color temperature inthe range of about 2600 degrees Kelvin (K) to about 6000 K. Additionalsingle-chip LED lamps may also be attached to the mounting plate 105 ina desired pattern to adjust the CRI and/or CCT of the output lightand/or to provide a particular ratio of white-emitting multi-chip LEDlamps to colored single-chip LED lamps.

The light fixture 100 b also includes a control circuit 150 belectrically coupled to each of the multi-chip LED lamps 110 as well asthe single-chip LED lamps 106 r and 106 c, in a manner similar to thatdiscussed above with reference to FIG. 1A. The control circuit 150 b isconfigured to independently apply drive currents to the LED chips 103 ofthe multi-chip lamps 110 and/or to the single-chip LED lamps 106 rand/or 106 c to individually control the intensities of light providedthereby, for example using PWM and/or other control schemes as are wellknown in the art. In addition, although not illustrated in FIG. 1B, thelight fixture 100 b may further include one or more heat spreadingcomponents for spreading and/or removing heat emitted by the single-chipand/or multi-chip LED lamps, as also discussed above with reference toFIG. 1A.

LED light fixtures according to some embodiments of the presentinvention, such as the LED light fixtures 100 a and/or 10 b, may providea number of features and/or benefits. For example, LED light fixturesincluding multiple multi-chip lamps according to some embodiments of thepresent invention may provide a relatively high luminous efficacy (asexpressed in lumens per watt) for a given CRI. More particularly,conventional light fixtures may offer 10-20 lumens per watt for a CRI of90, while LED light fixtures according to some embodiments of thepresent invention may offer 60-85 lumens per watt for the same CRI. Inaddition, LED light fixtures according to some embodiments of thepresent invention may offer greater lumens per watt per square inch thanconventional light fixtures. As such, although light fixtures includingmulti-chip LED lamps according to some embodiments of the presentinvention may be more costly than those including comparable single-chiplamps, the cost per lumen may be significantly less. Also, the CRI maybe adjusted by using different combinations of single-chip LED lampcolors with the multi-chip LED lamps. For example, the ratio ofwhite-emitting LED lamps to single-chip color LED lamps may be about 2:1to about 4:1 depending on fixture size, desired CRI, and/or desiredcolor point. For larger area troffer fixtures, a ratio of greater thanabout 10:1 may be desired. In addition, LED lamps and/or light fixturesaccording to some embodiments of the present invention may bemanufactured using off-the-shelf components, and as such, may be morecost-effective to produce.

Although FIGS. 1A and 1B illustrates examples of LED light fixturesaccording to some embodiments of the present invention, it will beunderstood that the present invention is not limited to suchconfigurations. For example, although illustrated in FIGS. 1A and 1B asattached to the same face of the mounting plate 105 as the LED chips103, it is to be understood that the control circuits 150 a and/or 150 bmay be attached to an opposite or back face of the mounting plate 105and/or may be provided in a separate enclosure in some embodiments ofthe present invention. In addition, fewer or more multi-chip LED lampsand/or single-chip LED lamps may be attached to the mounting plate 105,for example, depending on the desired light output. Also, althoughillustrated with reference to multi-chip lamps 110 including four LEDchips 103 per lamp, multi-chip lamps with fewer or more LED chips perlamp may also be used in multi-chip LED light fixtures according to someembodiments of the present invention. Moreover, the multi-chip LED lamps110 need not all be identical. For example, some of the multi-chip LEDlamps may include a red LED chip, a green LED chip, and a blue LED chip,while others may include two blue LED chips and a red LED chip.Additional configurations of multi-chip LED lamps will be discussed ingreater detail below with reference to FIGS. 2A-2D and 3A-3E.

FIGS. 2A-2D illustrate examples of multi-chip LED lamps that may be usedin light fixtures according to some embodiments of the presentinvention. Referring now to FIG. 2A, a multi-chip LED lamp 200 includesa common substrate or submount 201 including first and second diemounting regions 202 a and 202 b. The die mounting regions 202 a and 202b are each configured to accept an LED chip, such as a light emittingdiode, an organic light emitting diode, and/or a laser diode. As shownin FIG. 2A, first and second LED chips 203 b and 203 g are mounted onthe die mounting regions 202 a and 202 b of the submount 201,respectively. For example, the LED chips 203 b and/or 203 g may beEZBright®. LED chips manufactured by Cree, Inc. More particularly, asshown in FIG. 2A, the first LED chip 203 b is a blue LED chip configuredto emit light in a blue wavelength range (i.e., 440-470 nm), while thesecond LED chip 203 g is a green LED chip configured to emit light in agreen wavelength range (i.e., 495-570 nm). The blue and/or green LEDchips 203 b and/or 203 g may be InGaN-based blue and/or green LED chipsavailable from Cree, Inc., the assignee of the present invention.

In addition, as illustrated in FIG. 2A, one or more light conversionmaterials at least partially cover the blue LED chip 203 b. Moreparticularly, a yellow-emitting phosphor 206 y and a red-emittingphosphor 206 r at least partially cover the blue LED chip 203 b. Theyellow-emitting phosphor 206 y is configured to absorb at least aportion of the light emitted by the blue LED chip 203 b and re-emitlight in a yellow wavelength range, while the red-emitting phosphor 206r is configured to absorb at least a portion of the light emitted by theblue LED chip 203 b and re-emit light in a red wavelength range. Assuch, the blue and green LED chips 203 b and 203 g may be independentlyenergized and/or driven by a control circuit, such as the controlcircuit 150 a of FIG. 1A, such that white light is output by the LEDlamp 200. As an alternative, in some embodiments, the blue LED chip 203b may be covered by only the yellow-emitting phosphor 206 y, and the LEDchip 203 g may be a cyan LED chip at least partially covered by thered-emitting phosphor 206 r. Accordingly, the multi-chip LED lamp 200 ofFIG. 2A includes two LED chips 203 b and 203 g configured to emit lightof four different colors to provide the white light output.

FIG. 2B illustrates an LED lamp 205 according to some embodiments of thepresent invention including a common submount 201 having first, second,and third die mounting regions 202 a, 202 b, and 202 c, and blue, green,and red LED chips 203 b, 203 g, and 203 r respectively mounted on thedie mounting regions 202 a, 202 b, and 202 c. The red LED chip 203 r isconfigured to emit light in a red wavelength range (i.e., 610-630 nm),and may be an AlInGaP LED chip available from Epistar, Osram and others.The LED lamp 205 further includes a fourth die mounting region 202 d andfourth LED chip mounted on the fourth die mounting region 202 d,illustrated in FIG. 2B as a cyan LED chip 203 c. The cyan LED chip 203 cis configured to emit light in a cyan wavelength range (i.e., 485-515nm). The blue, green, red, and cyan LED chips 203 b, 203 g, 203 r and203 c may be independently energized and/or driven by a control circuit,such that the combination of the emitted light may provide while lightoutput from the LED lamp 205. The white light output from the LED lamp205 also includes additional light available in the cyan wavelengthrange as compared to the LED lamp 200 of FIG. 2A. In other words, thefourth LED chip 203 c may be used to improve color rendering and/orefficiency for the LED lamp 205 in particular wavelength ranges.However, it is to be understood that LED chips configured to emit lightin other wavelength ranges, such as in the amber wavelength range, maybe mounted on the fourth die mounting region 302 d depending on thedesired white light output for the LED lamp 205.

FIG. 2C illustrates an LED lamp 210 also including a common submount 201having three die mounting regions 202 a, 202 b, and 202 c. However, inFIG. 2C, three blue LED chips 203 b, 203 b′, and 203 b″ are mounted onthe die mounting regions 202 a, 202 b, and 202 c, respectively. Inaddition, a different conversion material at least partially covers eachof the blue LED chips 203 b, 203 b′, and 203 b″. More particularly, asshown in FIG. 2C, a yellow-emitting phosphor 206 y at least partiallycovers the blue LED chip 203 b, a red-emitting phosphor 206 r at leastpartially covers the blue LED chip 203 b′, and a green-emitting phosphor206 g at least partially covers the blue LED chip 203 b″. For example,the yellow-emitting phosphor 206 y may include yttrium aluminum garnet(YAG) crystals which have been powdered and/or bound in a viscousadhesive. The yellow-emitting phosphor 206 y may be configured toexhibit luminescence when photoexcited by the blue light emitted fromthe blue LED chip 203 b. In other words, the yellow-emitting phosphor206 y is configured to absorb at least a portion of the light emitted bythe blue LED chip 203 b and re-emit light in a yellow wavelength range(i.e., 570-590 nm). Similarly, the red-emitting phosphor 206 r isconfigured to absorb at least a portion of the light emitted by the blueLED chip 203 b′ and re-emit light in a red wavelength range (i.e.,610-630 nm), while the green-emitting phosphor 206 g is configured toabsorb at least a portion of the light emitted by the blue LED chip 203b″ and re-emit light in a green wavelength range (i.e., 495-570 nm). Assuch, the combination of light emitted by the three blue LED chips 203b, 203 b′, and 203 b″ and the light emitted by the phosphors 206 y, 206r, and 206 g may provide white light output from the LED lamp 210.

FIG. 2D illustrates an LED lamp 215 according to still furtherembodiments of the present invention. The LED lamp 215 similarlyincludes a common submount 201 having three die mounting regions 202 a,202 b, and 202 c. Two blue LED chips 203 b and 203 b′ are respectivelymounted on the die mounting regions 202 a and 202 b of the submount 301.In addition, a red LED chip 203 r is mounted on the third die mountingregion 202 c. A conversion material, illustrated as a yellow-emittingphosphor 206 y, at least partially covers the blue LED chip 203 b.Similarly, another conversion material, illustrated as a green-emittingphosphor 206 g, at least partially covers the blue LED chip 203 b′.However, the yellow-emitting phosphor 206 y and the green-emittingphosphor 206 g are not provided on the red LED chip 203 r. Accordingly,the combination of light emitted by the blue LED chips 203 b and 203 b′and the light emitted by the yellow-emitting phosphor 206 y and thegreen-emitting phosphor 206 g may provide white light, while the lightemitted by the red LED chip 203 r may improve the color renderingproperties of the light. In other words, the addition of the light fromthe red LED chip 203 r may make the light output by the LED lamp 215appear to be more “warm.” As an alternative, in some embodiments, theLED chip 203 r may be a green LED chip, and the phosphor 206 g may be ared-emitting phosphor.

Although FIGS. 2A-2D illustrate examples of multi-chip LED lamps thatmay be used in LED light fixtures according to some embodiments of thepresent invention, it will be understood that the present invention isnot limited to such configurations. For example, in some embodiments,one or more of the LED chips of the multi-chip LED lamps may be coveredby an encapsulant, which may be clear and/or may include lightscattering particles, phosphors, and/or other elements to achieve adesired emission pattern, color and/or intensity. While not illustratedin FIGS. 2A-2D, the LED lamps may further include reflector cupssurrounding the LED chips, one or more lenses mounted above the LEDchips, one or more heat sinks for removing heat from the lightingdevice, an electrostatic discharge protection chip, and/or otherelements. For example, in some embodiments, the submount 201 may includeone or more heat sinks.

FIGS. 3A-3F illustrate multi-chip LED lamps according to furtherembodiments of the present invention. The LED lamps of FIGS. 3A-3F maybe used in LED light fixtures according to some embodiments of thepresent invention, such as the LED light fixtures 100 a and 100 b ofFIGS. 1A and 1B. Referring now to FIG. 3A, an LED lamp 300 includes acommon substrate or submount 301 including first, second, and third diemounting regions 302 a, 302 b, and 302 c. The die mounting regions 302a, 302 b, and 302 c are each configured to accept an LED chip, such as alight emitting diode, an organic light emitting diode, and/or a laserdiode. As shown in FIG. 3A, first, second, and third LED chips 303 b,303 c, and 303 r are mounted on the die mounting regions 302 a, 302 b,and 302 c of the submount 301, respectively. For example, the LED chips303 b, 303 c, and/or 303 r may be EZBright® LED chips manufactured byCree, Inc. In some embodiments, the LED chips 303 b, 303 c, and 303 rmay be vertical devices including a cathode contact on one side the chipand an anode contact on an opposite side of the chip.

In addition, a conversion material at least partially covers the firstLED chip 303 b. For example, the conversion material may be a phosphor,polymer, and/or dye that is configured to absorb at least some of thelight emitted by the first LED chip 303 b and re-emit light of adifferent color. In other words, the conversion material may bephotoexcited by the light emitted from the first LED chip 303 b, and mayconvert at least a portion of the light emitted by the first LED chip303 b to a different wavelength. In FIG. 3A, the conversion material isillustrated as a yellow-emitting phosphor 306 y. In some embodiments,the yellow-emitting phosphor 306 y may be yttrium aluminum garnet (YAG).The yellow-emitting phosphor 306 y may be provided to cover the LED chip303 b using many different techniques. For example, the yellow-emittingphosphor 306 y may be included in an encapsulant material in a plasticshell surrounding the blue LED chip 303 b. In addition and/oralternatively, the yellow-emitting phosphor 306 y may be directly coatedon the blue LED chip 303 b itself, for example, as described in U.S.Pat. No. 7,217,583, assigned to the assignee of the present invention.In other techniques, the yellow-emitting phosphor 306 y may be coated onthe LED chip 303 b using spin coating, molding, screen printing,evaporation and/or electrophoretic deposition.

The LED chips 303 b, 303 e, and 303 r may be selected such that thethird LED chip 303 r emits light having a wavelength longer than that ofthe second LED chip 303 c, and such that the second LED chip 303 c emitslight having a wavelength longer than that of the first LED chip 303 b.The conversion material 306 y may be selected to emit light having awavelength between that of the second LED chip 303 c and the third LEDchip 303 r. More particularly, as shown in FIG. 3A, a blue LED chip 303b is mounted on the first die mounting region 302 a, a cyan LED chip 303c is mounted on the second die mounting region 302 b, and a red LED chip303 r is mounted on the third die mounting region 302 c. The blue LEDchip 303 b is configured to emit light within a blue wavelength range(i.e., about 440 to about 490 nm). The red LED chip 303 r is configuredto emit light within a red wavelength range (i.e., about 610 to about630 nm). The cyan LED chip 303 c is configured to emit light within acyan wavelength range that is between that of the blue and red LED chips303 b and 303 r, for example, about 485 to about 515 nm. In addition,the yellow-emitting phosphor 306 y is configured to emit light within awavelength range between that of the blue and red LED chips 303 b and303 r, for example, about 570 to about 590 nm. Alternatively, in someembodiments, the third LED chip 303 r may be a green LED chip configuredto emit light within a green wavelength range (i.e., about 495 to about570 nm).

Still referring to FIG. 3A, the blue, red, and cyan LED chips 303 b, 303r, and 303 c may be independently energized and/or driven by a controlcircuit, such as the control circuit 150 a of FIG. 1A, to provide adesired white light output from the LED lamp 300. For example, for warmwhite light applications, first, second, and third drive currents may beapplied to the blue, cyan, and red LED chips 303 b, 303 c, and 303 r ina ratio such that the correlated color temperature of the light emittedfrom the LED lamp 300 is about 2600 K to about 6000 K. The current ratiomay be a function of the brightness and/or wavelengths of light emittedby the respective LED chips and/or the brightness and/or wavelengths ofthe converted light from the conversion material(s) to achieve a desiredcolor point. In addition, the cyan LED chip 303 c and theyellow-emitting phosphor 306 y may provide light in the intermediatespectrum between the wavelengths of light emitted by the blue and redLED chips 303 b and 303 r, such that an average wavelength of thecombination of the light emitted by the LED lamp 300 is about 555 nm.More particularly, in some embodiments, the blue LED chip 303 b may emitlight having a peak wavelength of about 460 nm, red LED chip 303 r mayemit light having a wavelength of about 610 nm, the cyan LED chip 303 cmay emit light having a peak wavelength of about 505 nm, and theyellow-emitting phosphor 306 y may emit light having a peak wavelengthof about 580 nm. In contrast, conventional LED lamps including red,blue, and green LED chips may operate less efficiently at suchwavelengths, as discussed above. Also, the addition of the cyan LED chip303 c may improve the CRI of the LED lamp 300 as compared to aconventional lamp using a red LED chip in combination with a blue LEDchip coated with a yellow phosphor. For example, LED lamps according tosome embodiments of the present invention may have a CRI of about 90-99.

FIGS. 3B-3F illustrate alternate configurations of LED lamps accordingto some embodiments of the present invention. The LED chips of the lampsof FIGS. 3B-3E may have similar characteristics and/or may beindependently operated to provide white light having substantiallysimilar characteristics as those described above with reference to FIG.3A. Referring now to FIG. 3B, an LED lamp 305 includes a common submount301 having three die mounting regions 302 a, 302 b, and 302 c, and blue,cyan, and red LED chips 303 b, 303 c, and 303 r respectively mounted onthe die mounting regions 302 a, 302 b, and 302 c. The LED lamp 305further includes a fourth die mounting region 302 d and fourth LED chipmounted on the fourth die mounting region 302 d, illustrated in FIG. 3Bas another blue LED chip 303 b′. However, it is to be understood that,in some embodiments, LED chips configured to emit light of other colors,such as green and/or amber, may be mounted on the fourth die mountingregion 302 d. The first and fourth die mounting regions 302 a and 302 dare diametrically opposed on the submount 301. As such, the two blue LEDchips 303 b and 303 b′ are provided at diagonally opposite positions onthe submount 301. A yellow-emitting phosphor 306 y at least partiallycovers both of the blue LED chips 303 b and 303 b′; however, thephosphor 306 y is not provided on the red and cyan LED chips 303 r and303 c. Accordingly, the combination of the light emitted by the blue LEDchips 303 b and 303 b′ and the yellow-emitting phosphor 306 y mayproduce white light, and the diametrically opposed positions of the blueLED chips 303 b and 303 b′ may provide a more even light distribution.Also, the additional light emitted by the red and cyan LED chips 303 rand 303 c may improve the color rendering properties of the overalllight output of the LED lamp 305. As an alternative, in someembodiments, the LED chip 303 c may be a blue LED chip at leastpartially covered by a green or yellowish-green phosphor, such as LuAG(Lanthanide+YAG).

FIG. 3C also illustrates an LED lamp 310 including two diametricallyopposed blue LED chips 303 b and 303 b′, a cyan LED chip 303 c, and ared LED chip 303 r mounted on a common submount 301 in a manner similarto that of the LED lamp 305 of FIG. 3B. However, as shown in FIG. 3C, aconversion material containing a yellow-emitting phosphor 306 y at leastpartially covers all of the LED chips 303 b, 303 b′, 303 e, and 303 r onthe submount 301. For example, in some embodiments, the yellow-emittingphosphor 306 y may be configured to convert at least a portion of theblue light emitted from the blue LED chips 303 b and 303 b′ into yellowlight. In some embodiments, the conversion material may further includea red-emitting phosphor in addition to the yellow-emitting phosphor 306y.

FIG. 3D illustrates an LED lamp 315 including two diametrically opposedblue LED chips 303 b and 303 b′, a cyan LED chip 303 c, and a red LEDchip 303 r mounted on the submount 301 in a manner similar to that ofthe LED lamp 305 of FIG. 3B. A first conversion material, illustrated asa yellow-emitting phosphor 306 y, at least partially covers both of theblue LED chips 303 b and 303 b′ but is not provided on the red and cyanLED chips 303 r and 303 c. In addition, a second conversion material,illustrated as a red-emitting phosphor 306 r, at least partially coversall of the LED chips 303 b, 303 b′, 303 c, and 303 r on the submount301. For example, the red-emitting phosphor 306 r may be included alongwith yellow-emitting phosphor 306 y on blue LED chips 303 b and 303 b′to improve the color rendering characteristics of the light produced bythe blue LED chips 303 b and 303 b′. More particularly, the red phosphor306 r may also emit light in response to stimulation by light emitted bythe blue LED chips 303 b and 303 b′, and may thus provide an additionalred light emission complement to the overall light emitted by the LEDlamp 315. The resulting light may have a warmer appearance, which maygive objects a more natural appearance when illuminated.

However, the excitation curve of the red phosphor 306 r may overlap withthe emission curve of the yellow emitting phosphor 306 y, meaning thatsome light emitted by the yellow phosphor 306 y may be reabsorbed by thered phosphor 306 r, which may result in a loss of efficiency. As such,in some embodiments, the first and/or second conversion materials may beprovided in discrete phosphor-containing regions. For example, theyellow 306 y and red 306 r emitting phosphors may be provided in twoseparate discrete phosphor-containing regions, which may provideimproved separation of the different phosphors for warm white, UV/RGB,and other phosphor applications. Further, the discretephosphor-containing regions formed on the LED structure 315 may be incontact with adjacent phosphor-containing regions and/or may beseparated from adjacent phosphor-containing regions. For example, in awarm white LED application, red and yellow phosphors may be physicallyseparated to reduce reabsorption of yellow light by the red phosphors.

FIG. 3E similarly illustrates an LED lamp 320 including twodiametrically opposed blue LED chips 303 b and 303 b′, a cyan LED chip303 c, and a red LED chip 303 r mounted on the submount 301. A firstconversion material, illustrated as a yellow-emitting phosphor 306 y, atleast partially covers both of the blue LED chips 303 b and 303 b′ butis not provided on the red and cyan LED chips 303 r and 303 c, while asecond conversion material, illustrated as a red-emitting phosphor 306r, at least partially covers all of the LED chips 303 b, 303 b′, 303 c,and 303 r on the submount 301. In addition, third and fourth conversionmaterials 306 x and 306 z at least partially cover the cyan LED chip 303c and the red LED chip 303 r. For example, the third conversion material306 x may be configured to emit light in response to stimulation bylight emitted by the cyan LED chip 303 c, and the fourth conversionmaterial 306 z may be configured to emit light in response tostimulation by the red LED chip 303 r to further improve the colorrendering characteristics of the light emitted by the LED lamp 320. Forexample, the third and/or fourth conversion materials 306 x and 306 zmay be a blue emitting phosphor, such as BAM (BaMgAl₂O₃). In someembodiments, the phosphors 306 y, 306 r, 306 x, and/or 306 z may beprovided in discrete phosphor-containing regions, as described above. Assuch, multiple phosphors of different colors may be arranged in adesired pattern on a chip to provide a desired emission pattern.

FIG. 3F illustrates an LED lamp 325 including two diametrically opposedblue LED chips 303 b and 303 b′ and two diametrically opposed cyan LEDchips 303 c and 303 e′ mounted on the submount 301. A first conversionmaterial, illustrated as a yellow-emitting phosphor 306 y, at leastpartially covers both of the blue LED chips 303 b and 303 b′ but is notprovided on the cyan LED chips 303 c and 303 e′. Similarly, a secondconversion material, illustrated as a red-emitting phosphor 306 r, atleast partially covers both of the cyan LED chips 303 c and 303 c′ butis not provided on the blue LED chips 303 b and 303 b′. Thus, the LEDchip coverage of the yellow and red-emitting phosphors 306 y and 306 rmay not overlap in some embodiments. The yellow-emitting phosphor 306 ymay emit light in response to stimulation by light emitted by the blueLED chips 303 b and 303 b′ such that the combined light output has agreen appearance, and the red phosphor 306 r may emit light in responseto stimulation by light emitted by the cyan LED chips 303 c and 303 c′such that the combined light output has an orange appearance.Accordingly, the combination of orange and green light emitted by theLED lamp 325 may provide a white light output having a warmerappearance.

Although FIGS. 3A-3F illustrate exemplary multi-chip LED lamps accordingto some embodiments of the present invention, it will be understood thatsome embodiments of the present invention are not limited to suchconfigurations. For example, although the LED lamps of FIGS. 3B-3Fillustrate that two out of the four LED chips in each lamp are blue LEDchips, it is to be understood that four LED chips of different colorsmay be provided. More particularly, in some embodiments, one of the blueLED chips may be replaced with a green and/or an amber LED chipdepending on the desired white light output. More generally, otherpermutations of three or more LED chips on a common submount and one ormore phosphors covering one or more of the LED chips may be included insome embodiments of the present invention. In addition, the ratio of thedrive currents for the individual LED chips may be adjusted to shift thechromaticity and/or color temperature of the white light output by theLED lamp along the blackbody locus. In other words, by adjusting theluminous intensity ratio of the blue, cyan, and red LED chips, the colortemperature of the white light can be changed. Also, in someembodiments, the LED chips of the multi-chip LED lamps may be covered byan encapsulant, which may be clear and/or may include light scatteringparticles, phosphors, and/or other elements to achieve a desiredemission pattern, color and/or intensity. While not illustrated in FIGS.3A-3F, the LED lamps may further include reflector cups surrounding theLED chips, one or more lenses mounted above the LED chips, one or moreheat sinks for removing heat from the lighting device, an electrostaticdischarge protection chip, and/or other elements. For example, in someembodiments, the submount 301 may include one or more heat sinks.

Tables 1 and 2 illustrate experimental results for color rendering index(CRI) and color quality scale (CQS) values that may be achieved bytypical LED lamps, such as those including one or more blue LED chips atleast partially covered by a yellow-emitting phosphor.

TABLE 1 CRI Values R1 69.4 Brown R2 84.0 Green-Brown R3 93.1Green-Yellow R4 64.5 Green R5 67.0 Cyan R6 74.4 Blue R7 80.1 Purple R851.1 Pink R9 −10.9 Strong Red R10 60.3 Strong Yellow R11 53.7 StrongGreen R12 47.5 Strong Blue R13 72.0 Caucasian skin R14 95.9 Foliage Ra73.0

More particularly, Table 1 illustrates the color rendering index valuesR1 through R14 of fourteen test colors used to calculate a general colorrendering index Ra. The color rendering index values R1 through R8, R13,and R14 illustrate degrees of subtle differences between naturallyreproduced colors with intermediate degrees of saturation. In contrast,the special color rendering index values R9 through R12 illustratedegrees of differences between strong and/or brilliantly reproducedcolors. As shown in Table 1, the overall color rendering index for atypical LED lamp may be about 73.0.

TABLE 2 CQS Values VS1 76.0 Purple VS2 95.2 Blue VS3 71.3 Cyan VS4 61.9VS5 67.3 VS6 68.4 VS7 69.7 VS8 77.4 Green VS9 94.3 VS10 82.0 Yellow VS1174.7 VS12 73.3 VS13 74.4 Orange VS14 66.6 Red VS15 69.7 CQS 73.1

Similarly, Table 2 illustrates the color quality scale values VS1through VS15 of seven test colors used to calculate an overall colorquality scale (CQS) value according to the National Institute ofStandards and Technology (NIST). As shown in Table 2, the general colorquality scale value for a typical LED lamp may be about 73.1. Thus, LEDlamps according to some embodiments of the present invention may enablehigher color rendering performance under both the CRI and CQSperformance standards.

FIG. 4A is a graph illustrating an example of a spectral distribution oflight that may be produced by an LED lamp according to some embodimentsof the present invention, such as the LED lamp 300 of FIG. 3A. In FIG.4A, the x-axis indicates the wavelength in nanometers (nm), while they-axis indicates the luminous intensity. As shown in FIG. 4, thespectral distribution of the LED lamp 300 includes blue (B), cyan (C),and red (R) emission spectra 499 b, 499 c, and 499 r, and emissionspectrum 499 y at a wavelength between cyan and red (e.g., yellow). Theblue spectrum 499 b represents the emission of the blue LED chip 303 b,the cyan spectrum 499 c represents the emission of the cyan LED chip 303c, and the red spectrum 499 r represents the emission of the red LEDchip 303 r. The spectrum 499 y represents the luminescence that isexhibited by a light conversion material, such as the yellow-emittingphosphor 306 y, when photoexcited by the emission of the blue LED chip303 b.

The white light emitted by the LED lamp 300 can be characterized basedon the peak wavelengths of the emission spectra 499 b, 499 e, 499 r, and499 y of the respective blue, cyan, and red LED chips 303 b, 303 c, and303 r and the phosphor 306 y. As illustrated in FIG. 4A, the blue LEDchip 303 b emits light having a peak wavelength of about 460 nm, whilethe red LED chip 303 r emits light having a peak wavelength of about 610nm, and the cyan LED chip 303 c emits light having a peak wavelength ofabout 505 nm. The light conversion material emits light having a peakwavelength between the peak wavelengths of the cyan and red LED chips303 c and 303 r. In addition, the luminous intensity of the emissionspectra 499 b, 499 c, 499 r, and 499 y may be adjusted by independentlyapplying particular drive currents to the respective blue, cyan, and redLED chips 303 b, 303 c, and 303 r.

Accordingly, the combined spectral distribution of the LED lamp 300includes the combination of the blue, cyan, and red emission spectra 499b, 499 c, and 499 r, and the emission spectrum 499 y. More particularly,as shown by the dashed line 400 a in FIG. 4A, the combination of thelight emitted from the lamp 300 has local peak wavelengths at about440-470 nm, 490-520 nm, 560-590 nm, and 610-630 nm. Also, inconventional LED lamps including red, blue, and green LED chips, theresultant white light may be uneven in color, as it may be difficult todiffuse and mix the respective colored emissions with outstandingmonochromatic peaks in such a manner as to produce the desired whitelight. In contrast, the LED lamp 300 uses the luminescence exhibited bythe phosphor 306 y when photoexcited by the emission of the blue LEDchip 303 b to provide the intermediate spectrum 499 y between thespectra 499 c and 499 r of the cyan and red LED chips 303 c and 303 r.As such, LED lamps according to some embodiments of the presentinvention may more evenly diffuse and/or mix the respective colors oflight, for example, to provide warm white light having a relatively highCRI.

FIG. 4B is a graph illustrating an example of a spectral distribution oflight that may be produced by an LED lamp according to some embodimentsof the present invention, such as the LED lamp 325 of FIG. 3F. In FIG.4B, the x-axis indicates the wavelength in nanometers (nm), while they-axis indicates the luminous intensity. As shown in FIG. 4B, thespectral distribution of the LED lamp 325 includes blue (B), cyan (C),yellow (Y) and red (R) emission spectra 499 b, 499 c, 499 y and 499 r.The blue spectrum 499 b represents the emission of the blue LED chips303 b and 303 b′, and the cyan spectrum 499 e represents the emission ofthe cyan LED chips 303 e and 303 e′. The spectrum 499 y represents theluminescence that is exhibited by a first light conversion material,such as the yellow-emitting phosphor 306 y, when photoexcited by theemission of the blue LED chips 303 b and/or 303 b′, while the spectrum499 r represents the luminescence that is exhibited by a second lightconversion material, such as the red-emitting phosphor 306 r, whenphotoexcited by the emission of the cyan LED chips 303 c and/or 303 e′

The white light emitted by the LED lamp 325 can be characterized basedon the peak wavelengths of the emission spectra 499 b, 499 c, 499 r, and499 y of the respective blue, cyan, and red LED chips 303 b, 303 c, and303 r and the phosphor 306 y. As illustrated in FIG. 4B, the blue LEDchips 303 b and 303 b′ emit light in a wavelength range of about 445 nmto about 470 nm (with a peak wavelength of about 460 mm), while the cyanLED chips 303 e and 303 c′ emit light in a wavelength range of about 495mm to about 515 mm (with a peak wavelength of about 505 nm). The firstand second light conversion materials emit light having respective peakwavelengths greater than that of the blue and cyan LED chips.

The combined spectral distribution of the LED lamp 325 includes thecombination of the blue, cyan, yellow and red emission spectra 499 b,499 c, 499 y, and 499 r, as shown by the dashed line 400 b in FIG. 4B.As discussed above, the white light output from conventional LED lampsincluding red, blue, and/or green LED chips may be somewhat uneven incolor, due to difficulties in diffusing and/or mixing the outstandingmonochromatic peaks of the respective colored emissions. In contrast,the LED lamp 325 uses the luminescence exhibited by the phosphors 306 yand 306 r when respectively photoexcited by the emissions of the blueLED chips 303 b and 303 b′ and the cyan LED chips 303 c and 303 c′ tomore evenly diffuse and/or mix the respective colors of light, and thusmay provide warmer and relatively higher CRI white light. In addition,the luminous intensity of the emission spectra 499 b, 499 c, 499 r, and499 y may be adjusted by independently applying particular drivecurrents to the blue LED chips 303 b and 303 b′ and cyan LED chips 303 cand 303 c′.

FIG. 5 is a chromaticity diagram illustrating an example of thechromaticity that may be provided by an LED lamp according to someembodiments of the present invention, such as the LED lamp 300 of FIG.3A. In FIG. 5, the gamut of all visible chromaticities is illustrated asa horseshoe-shaped figure. More particularly, the curved edge 500 of thegamut is called the spectral locus, and corresponds to monochromaticlight, with wavelengths listed in nanometers (nm). The straight edge 505on the lower part of the gamut is called the purple line. These colors,although they are on the border of the gamut, have no counterpart inmonochromatic light. Less saturated colors appear in the interior of thefigure with white at the center. All colors that can be formed by mixingany two colors will lie on a straight line connecting two points thatrepresent the two colors on the chromaticity diagram. In addition, allcolors that can be formed by mixing three colors can be found inside thetriangle formed by the corresponding points on the chromaticity diagram(and so on for multiple sources).

Accordingly, as shown in FIG. 5, the light emitted by the blue LED chip303 b has a peak wavelength of about 460 nm, the light emitted by thered LED chip 303 r has a peak wavelength of about 610 nm, and the lightemitted by the cyan LED chip 303 c has a peak wavelength of about 505nm. Also, the light emitted by the yellow-emitting phosphor 306 y has apeak wavelength of about 570 nm. Accordingly, the LED lamp 300 may beconfigured to emit light having correlated color temperatures within therange defined by the shaded area 515. In other words, the white lightproduced by mixing the emissions of the blue, cyan, and red LED chips303 b, 303 c, and 303 r along with the yellow emitting phosphor 306 yhas a chromaticity falling within the range 515. As shown in FIG. 5, therange 515 is located over a blackbody radiation locus (i.e., Planckianlocus) 510, and the chromaticity of the color-mixed light is not sodifferent from the blackbody radiation locus 510 in a wide correlatedcolor temperature range. In other words, the color of the light producedmay have a variable chromaticity in a relatively wide correlated colortemperature range. As a result, the general color rendering index of thelamp 300 can be increased. In particular, LED lamps according to someembodiments of the present invention may produce warm white light havinga correlated color temperature of about 2600 K to about 6000 K with arelatively high CRI of greater than about 90, and in some embodiments,greater than about 95.

In multi-chip LED lamps and light fixtures according to some embodimentsof the present invention, the intensities of the individual LED chipsmay be independently controlled. This can be accomplished, for example,by controlling the relative emission of the LED chips through control ofthe applied current. FIG. 6 is a flowchart illustrating operations forcontrolling the relative intensities of LED chips in LED lamps accordingto some embodiments of the present invention, such as the LED lamp 300of FIG. 3A, to provide high-CRI warm white light. More particularly, asshown in FIG. 6, first, second, and third drive currents are applied tothe blue, cyan, and red LED chips at Block 600 at a ratio such that thecombination of the light emitted from the blue, cyan, and red LED chipsprovides white light having a correlated color temperature of about 2600K to about 6000 K and a CRI of about 90 to about 99. Accordingly, bycontrolling the relative power applied to the respective LED chips, alarge range of flexibility may be available both for providing thedesired chromaticity and controlling the color output of the individualdevices. As such, LED light fixtures according to some embodiments ofthe invention may be provided that allow the end user to control therelative powers applied to the respective LED chips. In other words, theLED lamps of the fixture could be “tuned” by the user to achieve desiredcolors or hues from the lamps. This type of control can be provided byknown control electronics, for example, using sets of predeterminedcurrent ratios.

In addition, although not illustrated, multi-chip LED lamps according tosome embodiments of the present invention may also include lenses andfacets to control the direction of the lamp's emitting light andmixing/uniformity. Other components, such as those related to thermalmanagement, optical control, and/or electrical signal modificationand/or control, may also be included to further adapt the lamps to avariety of applications.

Furthermore, phosphors according to some embodiments of the presentinvention may be provided by a semiconductor material, such as a directbandgap semiconductor. More particularly, phosphors according to someembodiments of the present invention may include semiconductor materialshaving a narrower bandgap than that of the quantum wells of the LEDchips. Such direct bandgap phosphors may be provided in the form of afilm and/or a powder layer on an LED chip to provide a desired colorshift. For example, such a direct bandgap phosphor may be an InGaN layerhaving a greater percentage of In than that found in the quantum wellsof the LED chip. Other examples of direct bandgap semiconductors mayinclude GaAs (1.42 eV), AlGaAs having an Al percentage of less thanabout 45%, and/or InP (1.34 eV). Moreover, indirect bandgapsemiconductors may also be used as phosphors in some embodiments of thepresent invention, although such phosphors may provide reducedefficiency.

FIGS. 7A-7D illustrate example configurations of direct bandgapsemiconductor phosphors in combination with LED chips according to someembodiments of the present invention. As shown in FIG. 7A, two directbandgap semiconductor phosphors 706 a and 706 b (which may havedifferent light absorption and/or emission characteristics) can berespectively provided on two LED chips 703 a and 703 b. For example, thedirect bandgap semiconductor phosphors 706 a and 706 b may be formed ona substrate, such as a glass or sapphire substrate, and may thus bespatially separated from the two LED chips 703 a and 703 b by thesubstrate therebetween. In contrast, as shown in FIG. 7B, the phosphor706 a may be directly on the LED chip 703 a, and the phosphor 706 b maybe directly on the LED chip 703 b. Accordingly, as illustrated in FIGS.7A and 7B, the LED chips 703 a and 703 b according to some embodimentsof the present invention may include integrated wavelength conversionmaterials. Also, as shown in FIG. 7C, both of the direct bandgapsemiconductor phosphor layers 706 a and 706 b may be stacked on the LEDchips 703 a and 703 b and spatially separated therefrom by the substrate705. As a further alternative, at least one of the stacked phosphorlayers 706 a and/or 706 b may be directly on the LED chips 703 a and 703b, as shown in FIG. 7D. Other configurations and/or combinations ofdirect bandgap semiconductor phosphors and LED chips may also beprovided according to some embodiments of the present invention. Forexample, although illustrated above as completely covering the LED chips703 a and 703 b, the phosphor layers 706 a and/or 706 b may be providedas partially overlapping one or more of the LED chips 703 a and/or 703 bsuch that not all of the light emitted therefrom is directed toward thephosphor layers 706 a and/or 706 b. Accordingly, in some embodiments,the phosphor layers 706 a and/or 706 b may be used as the phosphors inthe light fixtures and/or lamps described above with reference to FIGS.2A-3F.

The direct bandgap semiconductor phosphors 706 a and 706 b may bedeposited on the LEDs 703 a and/or 703 b as thin films, for example,using Metal-Organic Chemical Vapor Deposition (MOCVD) and/or sputteringtechniques. The films may be deposited on a substrate (such as sapphireor glass), on the inside of a lens, and/or directly on the LED chips. Inaddition, the direct bandgap semiconductor phosphors 706 a and 706 b maybe grown on a substrate. The properties of the substrate upon which thefilm is grown and/or deposited, as well as the subsequent processingconditions, may be adjusted to provide the desired spectral output. Asubstrate including direct bandgap semiconductor phosphors according tosome embodiments of the present invention may be used as a carrier waferto support an LED, for example, where the substrate has been removed,and/or to support a semiconductor layer that has been separated from asubstrate. Care may be taken so that the thin film layers are notdamaged in subsequent processing. The phosphors 706 a and 706 b may alsobe provided in particle or powder form. For powder phosphors, the sizeand/or shape of the particles may also influence the desired spectraloutput.

Still referring to FIGS. 7A-7D, the size, stoichiometry, and/ormorphology of the direct bandgap semiconductor phosphors 706 a and 706 bmay be selected to provide a desired spectral output. For example, thestoichiometry of the phosphors 706 a and 706 b may be changed to alterthe color of the emitted light and/or the absorption probability. Moreparticularly, the probability of absorption of an incident photon maydepend on the stoichiometry, which may affect the bandgap and/or densityof states. For example, if the intrinsic energy level E is greater thanthe bandgap E_(g) of the phosphors 706 a and 706 b (for example,slightly greater than E_(g)), the density of states may be relativelysmall, and thus the probability of absorption may be relatively small.In contrast, if the intrinsic energy level E_(i) is large compared tothe bandgap E_(g), the density of states may be greater, and absorptionmay be more likely. The probability of absorption may also beproportional to the thickness of the phosphor layers 706 a and 706 b.

Accordingly, the stoichiometry of the phosphors 706 a and 706 b may beadjusted to achieve a desired level of absorption and/or spectraloutput. For example, where the phosphors 706 a and/or 706 b areIn_(x)Ga_(1-x)N layers, the value of x may be varied over the thicknessof the phosphor layers 706 a and/or 706 b to provide a broader emissionspectrum. In contrast, for a single (non-varying) composition, thespectral emission may be fairly narrow. The phosphor layers 706 a and/or706 b may be configured to absorb at least a portion of the lightemitted by the LED chips 703 a and/or 703 b and re-emit light atwavelengths greater than that of the light emitted by the LED chips 703a and/or 703 b. Moreover, in some embodiments, the stoichiometry of thephosphors 706 a and/or 706 b may be adjusted to reduce the range ofspectral emission. In other words, in some embodiments, the phosphors706 a and/or 706 b may be configured to absorb and not re-emit light ofparticular wavelengths in some embodiments, for example, to reduceand/or remove undesired colors of light, although it may be at theexpense of efficiency.

In some embodiments, the direct bandgap semiconductor phosphors 706 aand 706 b may include quantum well structures. As such, thestoichiometry of the absorption region may be altered to provide adesired probability of absorption, while the spectral output may bealtered by quantum well structures. For example, the number of wells,well width, well separation, well shape, and/or well stoichiometry maybe varied to improve color rendering and/or alter efficiency. In someembodiments, the region surrounding the quantum well may be tapered toguide and/or enhance diffusion into the well.

FIG. 8 illustrates examples of different well shapes for quantum wellstructures that may be used in direct bandgap semiconductor phosphorlayers according to some embodiments of the present invention. Moreparticularly, FIG. 8 illustrates well structures having different wellshapes, well widths, well depths, and/or well separation. The wellstructures may employ stepwise grading, continuous grading, and/or othertechniques to provide a desired bandgap. As shown in FIG. 8, based onthe incident light 800, electrons 801 e-804 e at the conduction-band cancombine directly with holes 801 h-804 h at the valence band such thatthe energy of the recombination across the respective bandgaps 801 g-804g may be emitted as output light 805. The number and/or shapes of thewells shown in FIG. 8 may be modified to achieve a desired spectraloutput for a given spectral input. For example, the quantum well widthmay be modified by adjusting the quantum well growth time, changing thegrowth temperature, and/or adjusting the partial pressures of thechamber gases. Also, the well stoichiometry may be adjusted by changingthe gas partial pressures and/or other growth parameters. Changes suchas these may be made during growth of the quantum well to produce a wellwith nonuniform shape (i.e., varying stoichiometry).

Direct bandgap semiconductor phosphors according to some embodiments ofthe present invention may also be doped to alter their optical and/orelectrical properties. For example, dopants may be incorporated into thewells through the introduction of dopant source material into the growthchamber. In addition, direct bandgap semiconductor phosphors accordingto some embodiments of the present invention may be provided asconductors, for example, for electrical contacts.

The foregoing is illustrative of the present invention and is not to beconstrued as limiting thereof. Although a few exemplary embodiments ofthis invention have been described, those skilled in the art willreadily appreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe claims. Therefore, it is to be understood that the foregoing isillustrative of the present invention and is not to be construed aslimited to the specific embodiments disclosed, and that modifications tothe disclosed embodiments, as well as other embodiments, are intended tobe included within the scope of the appended claims. The invention isdefined by the following claims, with equivalents of the claims to beincluded therein.

What is claimed is:
 1. A solid state lamp comprising: a first solidstate emitter having peak emissions within a blue wavelength range; asecond solid state emitter having peak emissions within a cyanwavelength range; a first wavelength conversion material at leastpartially covering the first solid state emitter and arranged to emitlight within a yellow wavelength range; and a second wavelengthconversion material at least partially covering the second solid stateemitter and arranged to emit light within a red wavelength range.
 2. Thesolid state lamp of claim 1, comprising a third solid state emitterhaving peak emissions within the red wavelength range.
 3. The solidstate lamp of claim 1, comprising another solid state emitter havingpeak emissions within the blue wavelength range.
 4. The solid state lampof claim 1, comprising another solid state emitter having peak emissionswithin the cyan wavelength range.
 5. The solid state lamp of claim 1,further comprising a third wavelength conversion material at leastpartially converting any of the first solid state emitter and the secondsolid state emitter.
 6. The solid state lamp of claim 1, wherein each ofthe first solid state emitter and the second solid state emitter ismounted to a single mounting element.
 7. The solid state lamp of claim1, having light output of at least about 60 lumens per watt with a colorrendering index of at least
 90. 8. The solid state lamp of claim 1,wherein at least one of the first wavelength conversion material and thesecond wavelength conversion material at least partially covers all ofthe solid state emitters.
 9. The solid state lamp of claim 1,characterized by at least one of the following features (a) and (b): (a)the first wavelength conversion material only partially covers the firstsolid state emitter; and (b) the second wavelength conversion materialonly partially covers the second solid state emitter.
 10. The solidstate lamp of claim 1, wherein the first wavelength conversion materialand the second wavelength conversion material are segregated intodiscrete phosphor-containing regions.
 11. The solid state lamp of claim1, wherein each solid state lamp comprises a LED.
 12. The solid statelamp of claim 1, wherein any of the first wavelength conversion materialand the second wavelength material comprises a semiconductor phosphor.13. The solid state lamp of claim 1, comprising a control circuitconfigured to independently supply drive current to the first solidstate emitter and the second solid state emitter.
 14. A light fixturecomprising at least one solid state lamp according to claim
 1. 15. Asolid state lamp comprising: a plurality of solid state emittersincluding a first solid state emitter having peak emissions within ablue wavelength range, a second solid state emitter having peakemissions within a cyan wavelength range, and a third solid stateemitter having peak emissions within a green wavelength range; and afirst wavelength conversion material at least partially covering eachemitter of the plurality of solid state emitters and arranged to emitlight within a yellow wavelength range.
 16. The solid state lamp ofclaim 15, wherein the first wavelength conversion material onlypartially covers at least one emitter of the plurality of solid stateemitters.
 17. The solid state lamp of claim 15, further comprising asecond wavelength conversion material at least partially covering anysolid state emitter of the plurality of solid state emitters andarranged to emit light within a red wavelength range.
 18. The solidstate lamp of claim 17, wherein the second wavelength conversionmaterial only partially covers at least one solid state emitter of theplurality of solid state emitters.
 19. The solid state lamp of claim 15,comprising a control circuit configured to independently supply currentto each solid state emitter of the plurality of solid state emitters.20. A light fixture comprising at least one solid state lamp accordingto claim 15.